Odor-Taste Interactions in Food Perception: Exposure Protocol Shows No Effects of Associative Learning.

Repeated exposure can change the perceptual and hedonic features of flavor. Associative learning during which a flavor's odor component is affected by co-exposure with taste is thought to be central in this process. However, changes can also arise due to exposure to the odor in itself. The aim of this study was to dissociate effects of associative learning from effects of exposure without taste by repeatedly presenting one odor together with sucrose and a second odor alone. Sixty individuals attended two testing sessions separated by a 5-day Exposure Phase during which the stimuli were presented as flavorants in chewing gums that were chewed three times daily. Ratings of odor sweetness, odor pleasantness, odor intensity enhancement by taste, and odor referral to the mouth were collected at both sessions. Consistent with the notion that food preferences are modulated by exposure, odor pleasantness increased between the sessions independently of whether the odor (basil or orange flower) had been presented with or without sucrose. However, we found no evidence of associative learning in any of the tasks. In addition, exploratory equivalence tests suggested that these effects were either absent or insignificant in magnitude. Taken together, our results suggest that the hypothesized effects of associative learning are either smaller than previously thought or highly dependent on the experimental setting. Future studies are needed to evaluate the relative support for these explanations and, if experimental conditions can be identified that reliably produce such effects, to identify factors that regulate the formation of new odor-taste associations.

Binding of aldehydes to myofibrillar proteins as affected by two-step heat treatments.

BACKGROUND: The present study investigated the effect of two-step heat treatments on the structure of grass carp myofibrillar proteins (MPs) and their binding ability for selected aldehydes (hexanal, heptanal, octanal and nonanal). RESULTS: Within 30 min of the first heating step at 40 °C and 5-10 min of the second heating step at 90 °C, the enhancement of the flavor-binding ability was likely explained by the increases in surface hydrophobicity and total sulfhydryl content due to the unfolding of secondary structures of MPs through exposure of hydrophobic amino acids and sulfhydryl groups. Nevertheless, lengthy heating at 90 °C accelerated the aggregation of unfolded MPs and reduced the hydrophobic bonding sites, thus weakening the hydrophobic interactions and decreasing the resultant binding ability of MPs with aldehydes. CONCLUSION: The binding ability of aldehydes to MPs was found to be strongly influenced by changes in protein structure and surface during the two-step heating process. The results provided insight into improving the flavor characteristics of freshwater fish surimi products. © 2019 Society of Chemical Industry.

Multisensory flavor perception: The relationship between congruency, pleasantness, and odor referral to the mouth.

Our hedonic response to a food is determined by its flavor, an inherently multisensory experience that extends beyond the mere addition of its odor and taste. While congruency is known to be important for multisensory processes in general, little is known about its specific role in flavor processing. The aim of the present study was to delineate the effects of odor-taste congruency on two central aspects of flavor: odor referral (or mislocalization) to the mouth, and pleasantness. We further aimed to test whether an eventual effect on pleasantness was mediated by odor referral. Aqueous solutions containing odors and tastes were prepared to create food-like stimuli with varying degrees of congruency, ranging from maximally incongruent to maximally congruent in nine steps. Thirty participants reported where they perceived the odors, and how much they liked the solutions. Congruency had a positive linear effect both on odor referral to the oral cavity and on pleasantness. However, the effect of congruency on pleasantness was not mediated by odor referral. These results indicate that as an odor-taste mixture approximates a mental representation of a familiar food, its components are increasingly merged into one perceptual object sensed in the mouth. In parallel, the mixture is evaluated as increasingly pleasant, which promotes consumption of familiar foods that have been determined through experience to be non-toxic. While the modulatory role of congruency on pleasantness and odor referral was confirmed, our results also indicate that these effects arise through distinct perceptual mechanisms.

Effect of functional groups in strawberry flavoring on pea protein-flavor interactions: Potential applicable in flavor formulation for plant-based protein aqueous foods.

This research aimed to explore binding interactions between pea protein isolate (PPI) and selected strawberry flavorings including vanillin, γ-decalactone, furaneol, and (Z)-3-hexen-1-ol within an aqueous system. The results showed that binding affinities of PPI with all various functional group of flavor compounds decreased as temperature increased from 5 °C to 25 °C. Notably, at 25 °C, γ-decalactone displayed the highest binding affinity, followed by vanillin, (Z)-3-hexen-1-ol, and furaneol. Lowest binding was observed for furaneol, explained by its greater lipophilicity (lower partition coefficient values or LogP value) and molecular structure in each functional group in the flavor compounds. Thermodynamically, the interaction between PPI and each selected flavor compound was spontaneous, with evidence suggesting primary forces being hydrophobic interactions or hydrogen bonding/van der Waals forces. Computational molecular docking further confirmed these interaction types. This research provides insights into the interactions between PPI and strawberry flavorings, aiding in the selection of optimal flavor compound proportion for protein-rich products.

Physicochemical, structural, functional and flavor adsorption properties of white shrimp (Penaeus vannamei) proteins as affected by processing methods.

Proteins contribute to the flavor release and texture of foods besides their nutritional attributes. However, processing affects the protein structural conformation and, thus, their functional properties. White shrimp proteins (WSP) are well known for their nutritional and functional properties and limited attention has been paid to the flavor adsorption properties of WSP. This study investigated the effects of processing methods such as microwave drying, hot air drying, roasting, and boiling on the structural (secondary and tertiary) changes and physicochemical, functional, and flavor adsorption properties of white shrimp proteins (WSP). Structural changes of WSPs were evaluated by Fourier Transform Infrared (FTIR) spectroscopy, fluorescence spectroscopy, and sulfhydryl bond content. Results revealed that the processing triggered structural changes that affected the functional properties of WSP. The highest surface hydrophobicity (H0) of WSP in boiling (58.27 ± 1.68) and microwave drying (39.83 ± 0.83) caused increased emulsifying properties and decreased water solubility. The increased content of α-helix and random coils leads to cross-linking and protein aggregation in hot air drying (21.62 ± 0.37 %) and roasting (24.30 ± 0.24 %), which leads to low H0 and high foaming properties. Processing has increased the flavor adsorption ability of WSP. Among all the processing methods, boiling has shown the highest flavor adsorption potential, followed by microwave drying. The findings broaden the scope of techno-functional properties of WSP in the food industry by thermal treatment modification.

Unraveling the Role of Flavor Structure and Physicochemical Properties in the Binding Phenomenon with Commercial Food Protein Isolates.

Food protein-flavor binding influences flavor release and perception. The complexity of the binding phenomenon lies in the flavor and protein properties. Thus, molecular interactions between commercial whey- or plant-based protein isolates (PI) such as pea, soy, and lupin, with carbonyl and alcohol flavor compounds were assessed by static headspace (HS) GC-MS. HS results showed that not only the displacement of the carbonyl group from the inner part of the flavor structure toward the edge promoted binding up to 52.76% ± 4.65 but also the flavor's degree of unsaturation. Similarly, thermal treatment led to a slight increase in hexanal-protein binding because of possible protein conformational changes. Protein's residual fat (<1%) seemed insufficient to promote significant flavor binding to PI. Despite the complexity of commercial food protein isolates, the results displayed that binding is predominantly influenced by the flavor structure and physicochemical properties, with the protein source and residual fat playing a secondary role.

Effect of deacetylated konjac glucomannan on heat-induced structural changes and flavor binding ability of fish myosin.

This work investigated the effects of deacetylated konjac glucomannan (DKGM) on heat-induced structural changes and flavor binding in bighead carp myosin. DKGM could cross-link with fish myosin to form a thermostable complex and improve the gel strength of myosin. The incorporation of DKGM increased the surface hydrophobicity and total sulfhydryl content of heat-induced myosin. Increasing DKGM concentrations resulted in a decrease in the absolute zeta potential and a continuous increase in particle size. DKGM addition significantly reduced the α-helical content of myosin with a concomitant increase in ß-sheet, ß-turn, and random coil content. The binding abilities of myosin to flavors were significantly enhanced by increasing amounts of DKGM, attributing to the accelerative unfolding of myosin secondary structures and the exposure of additional hydrophobic and thiol binding sites. Increased numbers of available hydroxyl groups after DKGM treatment could also cause an increase of flavor adsorption by hydrogen bonding.

Gelatin enhances the flavor of chicken broth: A perspective on the ability of emulsions to bind volatile compounds.

The mechanism of flavor retention in chicken broth from the perspective of gelatin affecting the flavor-binding ability of emulsions was investigated. Results showed that fat was the important reservoir for aroma compounds in the emulsion. The particle sizes of emulsions significantly decreased with prolonged stewing time of gelatin, which was consistent with the results from confocal laser scanning microscopy and interfacial tension. The ability of pre-heated gelatin emulsions to bind volatile compounds with higher hydrophobicity was enhanced. When 0.1% gelatin was added into chicken broth, the total amount of the main volatile compounds (OAV > 1) increased from 458.83 ng/g to 1218.42 ng/g. In summary, the pre-heated gelatin increased the interfacial pressure of water/oil interface, resulting in a smaller particle size of oil droplets, and these further increased the binding area between oil droplets and flavor compounds. This appears to be the mechanism that gelatin enhances the flavor intensity of chicken broth.

Effect of malondialdehyde modification on the binding of aroma compounds to soy protein isolates.

The interactions of soy protein isolate (SPI) and flavor compounds (hexanal, trans-2-hexenal, 1-octen-3-ol, trans-2-octenal, nonanal, and trans-2-nonenal) were investigated. The influence of SPI structure modified by malondialdehyde (MDA) and flavor compound structure on the interactions were determined by using headspace solid-phase microextraction (SPME) and gas chromatography (GC) combined with mass spectrometry (MS). The binding of native SPI to the flavor compounds decreased in the order trans-2-nonenal>nonanal>trans-2-octenal>trans-2-hexenal>hexanal>1-octen-3-ol. It might be attributed to that aldehydes are more hydrophobic than alcohols. The former is more conducive to hydrophobic binding with the SPI. Furthermore, the aldehydes, in particular trans-s-undecenal, could also react covalently. The effect of MDA modification on protein-flavor interactions depended on the structure of the flavor compound. Upon low concentration of MDA (≤1mM), the binding of all six flavors to SPI increased. However, a further increase in the extent of MDA (≥2.5mM), more soluble and even insoluble aggregates formed, which reduced the binding of hexanal and nonanal to SPI. The other four flavors with double bond revealed little changes in binding (trans-2-octenal, and trans-2-nonenal) or even an increase in binding (trans-2-hexenal, and 1-octen-3-ol). The results suggested that hydrophobic interactions were weakened upon high extent of oxidation, whereas covalent interactions were enhanced.